Buggy code:
public abstract class MarkupContainer extends Component { private static final long serialVersionUID = 1L ; private static final Logger log = LoggerFactory . getLogger ( MarkupContainer . class ) ; private Object children ; private transient MarkupStream markupStream ; public MarkupContainer ( final String id ) { } public MarkupContainer ( final String id , IModel model ) { } public final MarkupContainer add ( final Component child ) { } public final MarkupContainer addOrReplace ( final Component child ) { } public final boolean autoAdd ( final Component component , final MarkupStream markupStream ) { } public final boolean autoAdd ( final Component component ) { } public final boolean contains ( final Component component , final boolean recurse ) { } public final Component get ( final String path ) { } public MarkupStream getAssociatedMarkupStream ( final boolean throwException ) { } public final MarkupStream getMarkupStream ( ) { } public String getMarkupType ( ) { } public void internalAdd ( final Component child ) { } public boolean isTransparentResolver ( ) { } public final Iterator iterator ( ) { } public final Iterator iterator ( Comparator comparator ) { } public final IResourceStream newMarkupResourceStream ( Class containerClass ) { } public void remove ( final Component component ) { } public final void remove ( final String id ) { } public final void removeAll ( ) { } public final void renderAssociatedMarkup ( final String openTagName , final String exceptionMessage ) { } public final MarkupContainer replace ( final Component child ) { } public Component setModel ( final IModel model ) { } public final int size ( ) { } public String toString ( ) { } public String toString ( final boolean detailed ) { } public final Object visitChildren ( final Class clazz , final IVisitor visitor ) { } public final Object visitChildren ( final IVisitor visitor ) { } private final void addedComponent ( final Component component ) { if ( component == ( this ) ) { throw new IllegalArgumentException ( "Component<seq2seq4repair_space>can't<seq2seq4repair_space>be<seq2seq4repair_space>added<seq2seq4repair_space>to<seq2seq4repair_space>itself" ) ; } MarkupContainer parent = component . getParent ( ) ; if ( parent != null ) { parent . remove ( component ) ; } component . setParent ( this ) ; final Page page = findPage ( ) ; if ( ( page != null ) && ( page . isAttached ( ) ) ) { component . attach ( ) ; } final IDebugSettings debugSettings = Application . get ( ) . getDebugSettings ( ) ; <START_BUG> if ( debugSettings . getComponentUseCheck ( ) ) { <END_BUG> component . setMetaData ( ADDED_AT_KEY , Strings . toString ( component , new MarkupException ( "added" ) ) ) ; } if ( page != null ) { page . componentAdded ( component ) ; } if ( isPreparedForRender ( ) ) { component . beforeRender ( ) ; } } private final void children_add ( final Component child ) { } private final Component children_get ( int index ) { } private final Component children_get ( final String id ) { } private final int children_indexOf ( Component child ) { } private final Component children_remove ( Component component ) { } private final Component children_remove ( int index ) { } private final Component children_set ( int index , Component child ) { } private final int children_size ( ) { } private final Component put ( final Component child ) { } private final void removedComponent ( final Component component ) { } private final void renderNext ( final MarkupStream markupStream ) { } protected final MarkupStream findMarkupStream ( ) { } protected void onComponentTagBody ( final MarkupStream markupStream , final ComponentTag openTag ) { } protected void onRender ( final MarkupStream markupStream ) { } protected void renderAll ( final MarkupStream markupStream ) { } protected final void renderComponentTagBody ( final MarkupStream markupStream , final ComponentTag openTag ) { } protected final void setMarkupStream ( final MarkupStream markupStream ) { } final void internalAttach2 ( ) { } void detachChildren ( ) { } void internalMarkRendering ( ) { } private Component [ ] copyChildren ( ) { } void onBeforeRenderChildren ( ) { } void onAfterRenderChildren ( ) { } public boolean hasAssociatedMarkup ( ) { } }

Fix:
if ( debugSettings . isLinePreciseReportingOnAddComponentEnabled ( ) ) {